JP7438596B2 - A negative electrode active material, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode - Google Patents

Description

[Cross reference to related applications]
This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0148837 filed on November 9, 2017, and all contents disclosed in the documents of the Korean patent application are , included as part of this specification.

The present invention relates to a negative electrode active material, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode, and specifically, the negative electrode active material includes spherical carbon-based particles and the spherical carbon-based particles. a carbon layer disposed thereon and containing nanoparticles, the nanoparticles comprising a silicon core; an oxide film layer disposed on the silicon core and containing SiO _x (0<x≦2); A coating layer containing LiF covers at least a portion of the surface of the oxide film layer.

The rapid increase in the use of fossil fuels has increased the demand for the use of alternative and clean energy, and one of the most actively researched areas is the field of power generation and storage using electrochemical reactions.

Currently, a secondary battery is a typical example of an electrochemical element that utilizes such electrochemical energy, and the range of its use is increasingly expanding. Recently, with the development of technology and increasing demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased rapidly. Among them, many studies have been conducted on lithium secondary batteries with high energy density, that is, high capacity, and they have been commercialized and widely used.

Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and silicon-based particles having a large discharge capacity may be used as the negative electrode active material. However, silicon-based particles such as SiO _x (0≦x<2) have low initial efficiency, and their volume changes excessively during the charging/discharging process, causing side reactions with the electrolyte. Therefore, a problem arises in that the life and stability of the battery are reduced.

In the past, in order to solve such problems, there have been attempts to combine a carbon-based material with high initial efficiency and silicon-based particles (Korean Patent Publication No. 10-2015-0112746).

However, despite the above-mentioned attempts, the problem of side reactions between silicon-based particles and electrolyte solution has not been smoothly resolved, and volume expansion has not been easily controlled. As a result, battery life and stability have not been effectively improved.

Therefore, there is a need for a negative electrode active material that can effectively control volume expansion during charging/discharging and side reactions with an electrolyte while enabling high battery capacity and high initial efficiency.

Korean Published Patent No. 10-2015-0112746

One problem to be solved by the present invention is to use a negative electrode active material that can effectively control volume expansion during charging/discharging and side reactions with the electrolyte while enabling high capacity and high initial efficiency of the battery. , a negative electrode including the same, and a secondary battery including the negative electrode.

According to an embodiment of the present invention, the nanoparticles include spherical carbon-based particles and a carbon layer disposed on the spherical carbon-based particles and containing nanoparticles, and the nanoparticles include a silicon core and the nanoparticles. A negative electrode active material is provided that includes an oxide film layer disposed on a silicon core and containing SiO _x (0<x≦2), and a coating layer containing LiF and covering at least a part of the surface of the oxide film layer. Ru.

According to other embodiments of the present invention, a negative electrode including the negative electrode active material and a secondary battery including the negative electrode are provided.

According to the negative electrode active material according to an embodiment of the present invention, the initial efficiency and discharge capacity of the battery can be improved by the coating layer containing LiF, and the side reactions between the negative electrode active material and the electrolyte and the volume expansion of the negative electrode active material can be reduced. can be effectively controlled. Moreover, the spherical carbon-based particles can further improve the discharge capacity of the battery.

FIG. 1 is a schematic diagram of a negative electrode active material of the present invention. FIG. 2 is a schematic diagram of first particles contained in a negative electrode active material according to the present invention. 1 is a ToF-SIMS result graph of Example 1 and Comparative Example 1.

Hereinafter, the present invention will be explained in more detail to deepen the understanding of the present invention.

The terms and words used in this specification and the claims are not to be construed to be limited to their ordinary or dictionary meanings, and are intended to be used by the inventors to best describe their invention. In accordance with the principle that the concept of a term can be defined as appropriate, the meaning and concept of the term should be interpreted in accordance with the technical idea of the present invention.

The terminology used herein is used to describe exemplary embodiments only and is not intended to limit the invention. A singular expression includes a plural expression unless the context clearly has a different meaning.

As used herein, terms such as "comprising," "comprising," or "having" are used to specify the presence of implemented features, numbers, steps, components, or combinations thereof. It should be understood that this does not in itself exclude the possibility of the presence or addition of one or more other features, figures, steps, components or combinations thereof.

As shown in FIGS. 1 and 2, a negative active material 100 according to an embodiment of the present invention includes spherical carbon-based particles 120 and nanoparticles 110 disposed on the spherical carbon-based particles 120. The nanoparticles 110 include a silicon core 111, an oxide film layer 112 disposed on the silicon core and containing SiO _x (0<x≦2), and a carbon layer 130. A coating layer 113 containing LiF may be included, covering at least a portion of the surface.

The spherical carbon-based particles can improve the discharge capacity of the battery. Further, since the spherical carbon-based particles are spherical, stable capacity and efficiency of the battery can be ensured even if the silicon content is small. Here, spherical shape may mean not only a perfect spherical shape with a set of points with a constant distance from the center point to the surface, but also a shape that is round to some extent, and specifically means a shape that satisfies a certain degree of sphericity. do.

The spherical carbon-based particles may be at least one selected from the group consisting of natural graphite, artificial graphite, hard carbon, and soft carbon.

The sphericity of the spherical carbon-based particles may be from 0.5 to 1, specifically from 0.55 to 0.95, more specifically from 0.6 to 0.9. It's fine. When the above range is satisfied, agglomeration of the nanoparticles is suppressed, stable capacity, life and efficiency of the battery can be ensured, and the rate of change in the thickness of the electrode can be reduced. The sphericity may be measured by a particle analyzer (QICPIC-LIXELL, Sympatec GmbH). Specifically, after deriving the cumulative distribution of the sphericity of the spherical carbon-based particles using a particle analyzer, the sphericity of the spherical particles with a distribution ratio of 50% from particles with a large sphericity is determined. This can be determined as the sphericity of carbon-based particles.

Preferably, when the spherical carbon-based particles are natural graphite, the sphericity may be from 0.7 to 1, specifically from 0.75 to 0.9. When the spherical carbon-based particles are natural graphite and satisfy the above range, agglomeration of the nanoparticles is suppressed, stable capacity, life and efficiency of the battery can be ensured, and the rate of change in electrode thickness is reduced. obtain.

The average particle diameter (D ₅₀ ) of the spherical carbon-based particles may be from 2 μm to 50 μm, specifically from 3 μm to 30 μm, and more specifically from 5 μm to 20 μm. When the above range is satisfied, the negative electrode active material can be easily manufactured and the battery can be charged/discharged effectively. The average particle size (D ₅₀ ) in this specification can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle diameter (D ₅₀ ) can be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes in the submicron range to several millimeters, and can provide results with high reproducibility and high resolution.

The spherical carbon-based particles may be included in an amount of 40% to 95% by weight, specifically 50% to 93% by weight, based on the total weight of the negative electrode active material. In particular, it may be contained in an amount of 60% to 90% by weight. When the above range is satisfied, the phenomenon in which the carbon-based particles aggregate in the form of secondary particles can be suppressed, so that it may be easy to manufacture the desired negative electrode active material.

The carbon layer may be disposed on the spherical carbon-based particles. Specifically, the carbon layer may exist in a form that covers at least a portion of the spherical carbon-based particles, and more specifically, the carbon layer covers all of the spherical carbon-based particles. May exist in the form

The carbon layer may include at least one of amorphous carbon and crystalline carbon.

The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotubes, and graphene.

The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress expansion of the nanoparticles. The amorphous carbon is at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a carbon-based material formed using hydrocarbon as a source of chemical vapor deposition. It may be.

The other carbonized organic substance may be a carbonized organic substance selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

The hydrocarbons may be substituted or unsubstituted aliphatic or cycloaliphatic hydrocarbons, substituted or unsubstituted aromatic hydrocarbons. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methine, ethene, ethylene, acetylene, propene, butane, butene, pentene, isobutene or hexane. The aromatic hydrocarbons of the substituted or unsubstituted aromatic hydrocarbons include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumaron, pyridine, anthracene, or phenanthrene. can be mentioned.

The carbon layer may be included in an amount of 0.5% to 50% by weight based on the total weight of the negative electrode active material, specifically, 2% to 35% by weight, and more specifically, may be included from 5% to 25% by weight. When the above range is satisfied, a conductive path can be effectively ensured. At the same time, the carbon layer can strengthen the bond between the nanoparticles and the spherical carbon-based particles, so that the nanoparticles can be effectively detached from the carbon-based particles during charging/discharging of the battery. can be prevented.

The thickness of the carbon layer may be 10 nm to 15 μm, specifically 15 nm to 10 μm, more specifically 20 nm to 8 μm. When the above range is satisfied, nanoparticles and carbon-based particles can be effectively composited.

The carbon layer may include nanoparticles. At least a portion of the nanoparticles may be in contact with the spherical carbon-based particles. The nanoparticles may not be exposed to the outside through the carbon layer, or at least some of the nanoparticles may be exposed to the outside.

The nanoparticles may include a silicon core, an oxide layer, and a coating layer.

The silicon core may include Si, and specifically may be made of Si. This can increase the capacity of the secondary battery.

The average particle size (D ₅₀ ) of the silicon core may be from 40 nm to 400 nm, specifically from 60 nm to 200 nm, and more specifically from 80 nm to 150 nm. When the above range is satisfied, the nano-sized silicon core will not be easily broken during charging/discharging of the battery, and lithium can be inserted and extracted effectively.

The oxide layer may be disposed on the silicon core. Specifically, the oxide film layer may cover at least a portion of the surface of the silicon core.

The oxide film layer may include SiO _x (0<x≦2), and specifically may include SiO ₂ . Accordingly, excessive volume change of the silicon core can be controlled during charging/discharging of the secondary battery.

The thickness of the oxide layer may be from 0.01 nm to 20 nm, specifically from 0.05 nm to 15 nm, and more specifically from 0.1 nm to 10 nm. When the above range is satisfied, excessive changes in the volume of the silicon core can be effectively controlled while maintaining the capacity of the secondary battery.

The coating layer may cover at least a portion of the surface of the oxide film layer. Specifically, the coating layer may be disposed to cover the entire surface of the oxide film layer, or may be disposed to cover only a portion of the surface.

The coating layer may contain LiF, and specifically may consist of LiF. LiF in the coating layer acts as a kind of SEI film to prevent side reactions between the silicon core and the electrolyte, improve lithium ion conductivity, and control excessive volume expansion of the silicon core. This can improve the initial efficiency of the negative electrode. Specifically, although not limited thereto, LiF included in the coating layer may be formed into a crystalline phase and an amorphous phase by heat treatment applied during manufacturing of the negative electrode active material. At this time, the lithium ion conductivity may be improved by the interface between the crystalline phase and the amorphous phase.

The LiF may be included in an amount of 0.01% to 25% by weight, specifically 0.05% to 12% by weight, based on the total weight of the negative electrode active material, and more specifically, Typically, it may be contained in an amount of 0.2% to 5% by weight. When the above range is satisfied, side reactions between the silicon core and the electrolyte can be effectively prevented, lithium ion conductivity can be effectively improved, and excessive volume expansion of the silicon core can be effectively controlled. This can effectively improve the initial efficiency of the negative electrode.

The thickness of the coating layer may be from 0.01 nm to 50 nm, specifically from 0.05 nm to 15 nm, more specifically from 0.1 nm to 10 nm. When the above range is satisfied, the effect of the coating layer described above may be further improved.

The oxide layer may further include lithium silicate. The lithium silicate may be formed when the oxide layer and coating layer in appropriate proportions are heat treated using a specific heat treatment temperature when forming the carbon layer. That is, it may be a byproduct formed by a reaction between the LiF and the oxide film layer. The lithium silicate can reduce the initial irreversibility of the battery, thereby improving the initial efficiency of the battery. The lithium silicate may include at least one of Li ₂ SiO ₃ , Li ₄ SiO ₄ , and Li ₂ Si ₂ O ₅ , and specifically may include Li ₂ SiO ₃ .

The nanoparticles may be included in an amount of 1% to 50% by weight, more specifically, 2% to 40% by weight, based on the total weight of the negative electrode active material, and more specifically, It may be included from 3% to 35% by weight. When the above range is satisfied, a smooth composite is formed with the spherical carbon-based particles, and side reactions between the negative electrode active material and the electrolyte can be reduced.

The weight ratio of the spherical carbon-based particles to the nanoparticles may be from 98:2 to 50:50, specifically from 97.5:2.5 to 55:45, more specifically. may be between 95:5 and 60:40. When the above range is satisfied, the capacity and efficiency of the battery can be stably ensured.

A method for manufacturing a negative electrode active material according to another embodiment of the present invention includes the steps of: preparing a silicon core on which an oxide film layer containing SiO _x (0<x≦2) is disposed; The method may include forming a coating layer containing LiF to form nanoparticles, and disposing a carbon layer containing the nanoparticles on spherical carbon-based particles.

In the step of preparing a silicon core on which an oxide film layer containing SiO _x (0<x≦2) is arranged, the oxide film layer can be formed by heat-treating the silicon core in oxygen or air. Alternatively, an oxide layer may be formed on the silicon core through a milling process. However, it is not necessarily limited to this.

In the step of forming a coating layer containing LiF on the oxide film layer to form nanoparticles, the coating layer may be formed by the following method.

The coating layer may be formed by milling, pulverizing, and mixing a silicon core on which the oxide film layer is formed together with LiF. Alternatively, after the silicon core is dispersed in a solvent, lithium acetate and ammonium fluoride may be mixed together to form the coating layer. Alternatively, the coating layer may be formed by disposing LiF on the oxide layer by sputtering. However, the method is not necessarily limited to the above method.

The step of disposing the carbon layer containing the nanoparticles on the spherical carbon-based particles may include the following method.

After preparing a mixed solution by dispersing the nanoparticles in a solvent, a slurry is prepared by dispersing the spherical carbon-based particles and an organic solution that can be pitch or a carbon source into the mixed solution. After the slurry is heat treated, it may be ground to form the carbon layer, and at the same time the nanoparticles may be included in the carbon layer. Alternatively, the carbon layer may be formed by subjecting the slurry to a spray drying process and then pulverizing it. Separately, only the nanoparticles and the spherical carbon-based particles are mixed, heat-treated to arrange the nanoparticles on the spherical carbon-based particles, and then chemical vapor deposition (CVD) is used. Alternatively, the carbon layer can be formed by mixing an organic material such as pitch and then carbonizing it. However, the method is not necessarily limited to the above method.

A negative electrode according to another embodiment of the present invention may include a negative active material, where the negative active material is the same as the negative active material of the embodiments described above. Specifically, the negative electrode may include a current collector and a negative electrode active material layer disposed on the current collector. The negative electrode active material layer may include the negative electrode active material. Further, the negative active material layer may further include a binder and/or a conductive material.

The current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. . Specifically, transition metals that adsorb carbon well, such as copper and nickel, can be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

The binder may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate. ate), polyvinyl alcohol, carboxymethyl cellulose (CMC) , starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, poly It can contain at least one selected from the group consisting of poly acrylic acid and substances in which these hydrogens are replaced with Li, Na, Ca, etc., and various copolymers thereof. May include coalescence.

The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity; for example, graphite such as natural graphite or artificial graphite; carbon black, acetylene black. Carbon blacks such as , Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powders. ; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives, etc. may be used.

A secondary battery according to another embodiment of the present invention may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof will be omitted.

The positive electrode may include a positive current collector, and a positive active material layer formed on the positive current collector and including the positive active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity; for example, stainless steel, aluminum, nickel, titanium, fired Carbon, aluminum, or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like may be used. Further, the positive electrode current collector may generally have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, and nonwoven body.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material includes layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), and compounds substituted with one or more transition metals; LiFe ₃ Lithium iron oxides such as O ₄ ; Lithium manganese oxides such as chemical formula Li _1+c1 Mn _2-c1 O ₄ (0≦c1≦0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxides ( Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ ; chemical formula LiNi _1-c2 M _c2 O ₂ (where M is Co, Mn, Al, Ni-site type lithium nickel oxide, which is at least one selected from the group consisting of Cu, Fe, Mg, B, and Ga and satisfies 0.01≦c2≦0.3; chemical formula: LiMn _2-c3 M _c3 O ₂ (here, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01≦c3≦0.1 ) or Li ₂ Mn ₃ MO ₈ (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); Examples include, but are not limited to, LiMn ₂ O ₄ in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion. The positive electrode may be made of Li-metal.

The cathode active material layer may include a cathode conductive material and a cathode binder in addition to the cathode active material described above.

At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and there are no special restrictions as long as it has electrical conductivity without causing a chemical change in the constructed battery. Available for use. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; copper, nickel, Examples include metal powders or metal fibers such as aluminum and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. One type may be used alone or a mixture of two or more types may be used.

Further, the positive electrode binder plays a role of improving adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl Examples include cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these may be used alone or a mixture of two or more may be used.

The separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular restrictions as long as it is normally used as a separator in lithium secondary batteries. A material that has low resistance to ion migration and excellent electrolyte impregnation ability is suitable. Specifically, porous polymer films, for example, polyolefin-based films such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, etc. Porous polymer films made of polymers or laminated structures of two or more layers thereof can be used. Further, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc., may be used. Further, in order to ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric substance may be used, and may optionally be used as a single layer or multilayer structure.

Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries. It is not limited to.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran. , dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl- Aprotic organic solvents such as 2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc. may be used.

In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably used because they are highly viscous organic solvents and have a high dielectric constant, so they easily dissociate lithium salts. If carbonate is mixed with a linear carbonate of low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte with high electrical conductivity can be produced, so it is more preferably used. good.

The metal salt may be a lithium salt, and the lithium salt is a substance suitable for dissolution in the non-aqueous electrolyte, and for example, anions of the lithium salt include F ⁻ , Cl ⁻ , I ⁻ , NO ₃ ⁻ , N(CN) ₂ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , (CF ₃ ) ₂ PF ₄ ⁻ , (CF ₃ ) ₃ PF ₃ ⁻ , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may be used.

In addition to the constituent components of the electrolyte, the electrolyte may contain, for example, difluoroethylene carbonate, etc., for the purpose of improving battery life characteristics, suppressing decrease in battery capacity, and improving battery discharge capacity. Haloalkylene carbonate compounds, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted One or more additives such as imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may further be included.

According to yet another embodiment of the present invention, a battery module including the secondary battery as a unit cell, and a battery pack including the same are provided. The battery module and the battery pack are selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system, since they include the secondary battery having high capacity, high rate-limiting characteristics, and high cycle characteristics. It can be used as a power source for medium- and large-sized devices.

In the following, preferred embodiments are presented for better understanding of the present invention. However, the following examples are merely illustrative of this description, and it is obvious to those skilled in the art that various changes and modifications can be made within the scope of this description and technical idea. Naturally, other variations and modifications fall within the scope of the claims.

[Examples and comparative examples]
Example 1: Manufacture of battery (1) Manufacture of negative electrode active material 4.1 g of silicon (Si) having a maximum particle size (D _max ) of 45 μm and 0.08 g of LiF were added to 30 g of isopropanol to prepare a mixed solution. Thereafter, the mixture was pulverized for 30 hours at a bead rotation speed of 1,200 rpm using zirconia beads (average particle size: 0.3 mm). At this time, the average particle diameter (D ₅₀ ) of the generated silicon is 100 nm, the thickness of SiO ₂ formed on the surface of the silicon is 10 nm, and the thickness of LiF disposed on the SiO ₂ is It was 0.1 nm to 10 nm.

Next, 20 g of spherical natural graphite with an average particle diameter (D ₅₀ ) of 15 μm and a sphericity of 0.8 and 3.3 g of solid phase pitch were added to the mixed solution and dispersed to produce a slurry. did.

The slurry and ethanol/water (volume ratio = 1:9) were mixed at a volume ratio of 1:10 to prepare a dispersion for spray drying. The dispersion was dried in a mini spray dryer (manufacturer: Buchi, model name: B-290 mini spray) under the conditions of an inlet temperature of 180°C, an aspirator of 95%, and a feeding rate of 12. It was spray-dried through a dryer). Thereafter, 20 g of the spray-dried mixture (composite) was heat-treated at 950° C. in a nitrogen atmosphere to prepare a negative active material. LiF (corresponding to the coating layer of the present invention) in the produced negative electrode active material is 0.3% by weight based on the total weight of the negative electrode active material, and the Li content is ICP and the F content is This is a value calculated by adding up the values measured by ion chromatography. Furthermore, the sphericity of the spherical natural graphite in the produced negative electrode active material was confirmed to be 0.7.

(2) Manufacture of negative electrode The negative electrode active material manufactured above, carbon black as a conductive material, carboxymethyl cellulose (CMC) as a binder, and styrene butadiene rubber (SBR) were mixed in a ratio of 95.8:1:1.7:1.5. A mixture was prepared by mixing in a weight ratio of . Thereafter, 7.8 g of distilled water was added to 5 g of the mixture and stirred to prepare a negative electrode slurry. The negative electrode slurry was applied to a 20 μm thick copper (Cu) metal thin film serving as a negative electrode current collector and dried. The temperature of the air circulated at this time was 60°C. Then, it was rolled and dried in a vacuum oven at 130° C. for 12 hours to prepare a negative electrode.

(3) Manufacture of secondary battery A lithium (Li) metal thin film obtained by cutting the manufactured negative electrode into a 1.7671 cm ² circle was used as a positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, and 0.5% by weight of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) was dissolved in a mixed solution with a volume ratio of 7:3. A lithium coin half-cell was manufactured by dissolving vinylene carbonate and injecting an electrolyte containing 1M LiPF ₆ dissolved therein.

Example 2: Production of battery (1) Production of negative electrode active material 4.1 g of silicon (Si) having a maximum particle size (D _max ) of 45 μm and 2.05 g of LiF were added to 30 g of isopropanol to produce a mixed solution. Thereafter, the mixture was pulverized for 30 hours using zirconia beads (average particle size: 0.3 mm) at a bead rotation speed of 1,200 rpm. At this time, the average particle size (D ₅₀ ) of the generated silicon is 100 nm, the thickness of SiO ₂ formed on the surface of the silicon is 10 nm, and the thickness of LiF disposed on the SiO ₂ is The range was from 0.1 nm to 30 nm.

Next, 20 g of spherical natural graphite with an average particle diameter (D ₅₀ ) of 15 μm and a sphericity of 0.8 and 3.3 g of solid phase pitch were added to the mixed solution and dispersed to produce a slurry. did.

The slurry and ethanol/water (volume ratio = 1:9) were mixed at a volume ratio of 1:10 to prepare a dispersion for spray drying. The dispersion was dried in a mini spray dryer (manufacturer: Buchi, model name: B-290 mini spray) under the conditions of an inlet temperature of 180°C, an aspirator of 95%, and a feeding rate of 12. It was spray-dried through a dryer). Thereafter, 20 g of the spray-dried mixture (composite) was heat-treated at 950° C. in a nitrogen atmosphere to prepare a negative active material. LiF (corresponding to the coating layer of the present invention) in the produced negative electrode active material is 7% by weight based on the total weight of the negative electrode active material, and the Li content is ICP and the F content is ion. This value is calculated by summing up the measurements by chromatography. Furthermore, the sphericity of the spherical natural graphite in the produced negative electrode active material was confirmed to be 0.7.

(2) Manufacture of negative electrode and secondary battery A negative electrode and secondary battery were manufactured in the same manner as in Example 1 except that the negative electrode active material was used.

Example 3: Production of battery (1) Production of negative electrode active material 4.1 g of silicon (Si) having a maximum particle size (D _max ) of 45 μm and 0.04 g of LiF were added to 30 g of isopropanol to produce a mixed solution. Thereafter, the mixture was pulverized for 30 hours using zirconia beads (average particle size: 0.3 mm) at a bead rotation speed of 1,200 rpm. At this time, the average particle size (D ₅₀ ) of the generated silicon is 100 nm, the thickness of SiO ₂ formed on the surface of the silicon is 10 nm, and the thickness of LiF disposed on the SiO ₂ is It was 0.1 nm to 5 nm.

Next, 20 g of spherical natural graphite with an average particle diameter (D ₅₀ ) of 15 μm and a sphericity of 0.8 and 3.3 g of solid phase pitch were added to the mixed solution and dispersed to produce a slurry. did.

The slurry and ethanol/water (volume ratio = 1:9) were mixed at a volume ratio of 1:10 to prepare a dispersion for spray drying. The dispersion was dried in a mini spray dryer (manufacturer: Buchi, model name: B-290 mini spray) under the conditions of an inlet temperature of 180°C, an aspirator of 95%, and a feeding rate of 12. It was spray-dried through a dryer). Thereafter, 20 g of the spray-dried mixture (composite) was heat-treated at 950° C. in a nitrogen atmosphere to prepare a negative active material. LiF (corresponding to the coating layer of the present invention) in the produced negative electrode active material is 0.15% by weight based on the total weight of the negative electrode active material, and the Li content is ICP and the F content is This value is calculated by adding up the values measured by ion chromatography. Furthermore, the sphericity of the spherical natural graphite in the produced negative electrode active material was confirmed to be 0.7.

(2) Manufacture of negative electrode and secondary battery A negative electrode and secondary battery were manufactured in the same manner as in Example 1 except that the negative electrode active material was used.

Example 4: Manufacture of battery A negative electrode active material was manufactured in the same manner as in Example 1, except that natural graphite with a sphericity of 0.65 was used in the manufacturing step of the negative electrode active material in Example 1. . LiF (corresponding to the coating layer of the present invention) in the produced negative electrode active material is 0.3% by weight based on the total weight of the negative electrode active material, and the Li content is ICP and the F content is This value is calculated by adding up the values measured by ion chromatography. Furthermore, the sphericity of the spherical natural graphite in the produced negative electrode active material was confirmed to be 0.6.

Comparative Example 1: Manufacture of battery (1) Manufacture of negative electrode active material In the manufacturing step of the negative electrode active material of Example 1, a negative electrode was manufactured in the same manner as in Example 1, except that LiF was not added at the time of manufacturing the slurry. An active material was produced.

(2) Manufacture of negative electrode and secondary battery A negative electrode and secondary battery were manufactured in the same manner as in Example 1 using the negative electrode active material.

Test Example 1: Evaluation of discharge capacity, initial efficiency, capacity retention rate, and electrode thickness change rate The batteries of Examples 1 to 4 and Comparative Example 1 were charged/discharged, and the discharge capacity, initial efficiency, and capacity retention rate were evaluated. and the electrode (negative electrode) thickness change rate were evaluated and are listed in Table 1 below.

On the other hand, charge/discharge was performed at 0.1C in the first cycle and second cycle, and charge/discharge was performed at 0.5C from the third cycle to the 49th cycle. The 50th cycle ended in a charged state (with lithium in the negative electrode), and after disassembling the battery and measuring the thickness, the electrode thickness change rate was calculated.
Charging conditions: CC (constant current)/CV (constant voltage) (5mV/0.005C current cut-off)
Discharge conditions: CC (constant current) conditions 1.5V

Discharge capacity (mAh/g) and initial efficiency (%) were derived from the results of one charge/discharge. Specifically, the initial efficiency (%) was derived by the following calculation.
Initial efficiency (%) = (discharge capacity after one discharge/one charge capacity) x 100

The capacity retention rate and the electrode thickness change rate were each derived by the following calculations.
Capacity retention rate (%) = (49 discharge capacity/1 discharge capacity) x 100
Electrode thickness change rate (%) = (Final negative electrode thickness change/initial negative electrode thickness) x 100

As shown in Table 1, Examples 1 to 4 were better than Comparative Example 1 in terms of discharge capacity, initial efficiency, capacity retention rate, and electrode thickness change rate. In the case of Comparative Example 1, since the negative electrode active material did not contain LiF, a conductive path was not ensured, so it seems that the initial efficiency and discharge capacity decreased. In addition, in the case of Example 1, since lithium silicate (Li ₂ SiO ₃ ) formed from LiF and SiO ₂ may exist in the negative electrode active material, the initial efficiency is lower than that in Comparative Example 1 in which the lithium silicate is not present. It seems that the discharge capacity and discharge capacity can be further improved (see Figure 3).

Claims (12)

Spherical natural graphite particles,
A negative electrode active material comprising a carbon layer containing nanoparticles disposed on the spherical natural graphite particles,
The sphericity of the spherical natural graphite particles is from 0.7 to 1,
The nanoparticles are
A silicon core having an average particle diameter (D ₅₀ ) of 100 nm or more and 400 nm or less,
an oxide film layer disposed on the silicon core and containing SiO _x (0<x≦2);
a coating layer containing LiF and covering at least a portion of the surface of the oxide film layer ,
The LiF is included in an amount of 0.2% to 5% by weight based on the total weight of the negative active material . The negative electrode active material according to claim 1, wherein the thickness of the oxide film layer is from 0.01 nm to 20 nm. The negative electrode active material according to claim 1 or 2 , wherein the coating layer has a thickness of 0.01 nm to 50 nm. The negative electrode active material according to any one of claims 1 to 3 , wherein the nanoparticles are contained in an amount of 1% to 50% by weight based on the total weight of the negative electrode active material. The negative electrode active material according to any one of claims 1 to 4 , wherein the spherical natural graphite particles have an average particle diameter (D ₅₀ ) of 2 μm to 50 μm. The negative electrode active material according to any one of claims 1 to 5 , wherein the spherical natural graphite particles are included in an amount of 40% to 95% by weight based on the total weight of the negative electrode active material. The negative electrode active material according to any one of claims 1 to 6 , wherein the weight ratio of the spherical natural graphite particles to the nanoparticles is from 98:2 to 50:50. The negative electrode active material according to any one of claims 1 to 7 , wherein the carbon layer is included in an amount of 0.5% to 50% by weight based on the total weight of the negative electrode active material. The negative electrode active material according to any one of claims 1 to 8 , wherein the oxide film layer further contains lithium silicate. The negative _electrode active material according to claim 9 , wherein _the lithium silicate includes at least one of _{Li2SiO3 , Li4SiO4 ,} and _Li2Si2O5 . A negative electrode comprising the negative electrode active material according to any one of claims 1 to 10 . A negative electrode according to claim 11 ;
a positive electrode;
a separator interposed between the positive electrode and the negative electrode;
A secondary battery containing an electrolyte.

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